The earthquake and tsunami that struck Japan last March created an estimated 25 million tons of debris, large amounts of which washed into the ocean. Soon after the disaster, satellites photographed and tracked large mats of wreckage—building parts, boats and household objects—floating off the Japanese coast. Now, according to computer models developed by Nikolai Maximenko and his colleagues at the University of Hawaii and at the U.S. National Oceanic and Atmo­spheric Administration, the detritus is on course to reach the north­western Hawaiian Islands early this year.

Given what is known about the hazards of floating refuse, scientists are taking the potential threat seriously. Already as much as 40 percent of the world's ocean surfaces harbor garbage that ranges in size from shipping containers to derelict fishing gear to small bits of plastic that can entangle or poison marine mammals. Researchers want to find out not only if the influx will threaten Hawaii but how it might interact with what is now out there.

Water and wind currents have broken up the tsunami wreckage so that it is no longer visible using NOAA's satellites, so the agency has been working to gain access to higher-resolution satellites to locate it. Later this year scientists affiliated with 5Gyres, a nonprofit that specializes in tracking and analyzing marine debris, will set sail across the North Pacific to investigate what is left of Japan's devastation.

Some scientists have already encountered tsunami rubble at sea. In September a Russian ship found a Japanese fishing vessel, a refrigerator, a television set and other household appliances bobbing west of Midway Atoll. In December large Japanese fishing floats washed up in Neah Bay in Wash­ington State and near Vancouver, B.C.

If these types of objects collide with the fragile coral reefs surrounding Hawaii's northwestern islands, the results could be catastrophic. Risks include physical damage to the reefs as well as the fouling of beaches that provide important habitats for albatross, Hawaiian monk seals, green sea turtles, and other threatened and endemic species. Hazardous materials are also a concern, although recent studies show the offshore impacts from debris contaminated with radiation have been minimal.

Nancy Wallace, director of NOAA's Marine Debris Program, says the agency is preparing for "best- and worst-case sce­narios." NOAA and other organizations have plans to cope with the debris, including any that may be contaminated. Whether or not tsunami wreckage makes landfall in significant vol­umes, however, it is somewhere at sea, adding to a serious and growing problem.

This article was published in print as "Remains of the Day."